This invention relates to magnetostrictive materials and more particularly to magnetostrictive materials prepared from amorphous magnetic alloys.
Both piezoelectric and magnetostrictive materials have been employed in the past as electromechanical transducers for sonar systems. In some applications the same element is used for transmitting and receiving. When the transmitting function is paramount a material capable of delivering high strains is desirable. Here PZT-4 or RFe.sub.2 (R=rare earth) materials are important. On the other hand, in many applications the receiving function is paramount, as in the case of listening (or passive) devices. This invention, while applicable to both transmitting and receiving functions, is primarily applicable to passive devices, such as hydrophones and pressure sensors, where saturation strains need not be huge.
The purpose of a hydrophone or pressure sensor is to convert small sound pressure differences into electrical signals. The important figure of merit (F) is: EQU F=s.sup.B k.sub.33.sup.2 /(1-k.sub.33.sup.2)
Here s.sup.B is the compliance of the material (e.g., the inverse of Young's modulus) at constant magnetic induction. k.sub.33.sup.2 is the square of the magnetomechanical coupling factor and is the fraction of energy converted to the total energy stored in the mechanical plus electrical systems. The magnetomechanical coupling factor is proportional to the change in magnetostriction with magnetic field (d.lambda./dH). As k.sub.33 exceeds 0.9 and approaches unity, the figure of merit increases very rapidly and approaches infinity.
A class of magnetic materials, amorphous magnetic alloys, with iron as the principal, has been under development for many years in the U.S. and abroad. A method to prepare ribbons of these alloys inexpensively has been developed by companies such as Allied Chemical and General Electric. One of the main motivations is to obtain an inexpensive material with high permeability and high magnetization. An important application is medium power (10 kW) transformers. For this and most common applications, a material with a low or near zero magnetostriction (.lambda.) is desirable (magnetostriction only causes hum and loss). For the magnetomechanical device, however, a high d .lambda./dH is desirable--generally the higher the better. Magnetostriction is necessary.
Heat treatments with both parallel and perpendicular field orientations have been used to improve the magnetomechanical coupling factors of amorphous metal alloy ribbons. Arai et al (IEEE Trans. on Magnetics MAG-12, 936 (1976)) treated ribbons of Fe.sub.80 P.sub.13 C.sub.7 and achieved a coupling factor of 0.53. Tsuya et al (J. Appl. Phys. 49, 1718 (1978)) achieved a coupling factor of 0.75 using Fe.sub.78 Si.sub.10 B.sub.12. Mitchell et al (IEEE Trans. on Magnetics MAG-4 1169 (1978)) and J. Appl. Phys. 50, 1627 (1979)) obtained coupling factors of 0.81-0.82 from Fe.sub.78 Si.sub.10 B.sub.12 and Fe.sub.71 Co.sub.9 B.sub.20. The highest magnetomechanical coupling factor of 0.85-0.86 was obtained by Brouha and van der Borst from Fe.sub.80 B.sub.15 Si.sub.5.
It would be desirable to find materials having still higher magnetomechanical coupling factors which would be used to provide improved sonar devices.